High strength corrosion resistant ferrous alloy sheets



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Watented Mar. l5, i938 I HIGH STRENGTH CORROSION RESISTANT FERROUS ALLOY SHEETS Victor ll. Lawrence, Norristown, Pa; assignor to Alan Wood Steel Company, a corporation of Pennsylvania No Drawing. Original application May 25, 1935,

Serial No. 23,520.

Divided and this application May 15, 1937, Serial No. 142,828

3 Claims.

This invention .relates to the production of rolled iron and steel sheets and plates characterized by relatively high resistance to rust and corrosion, and having high tensile strength and ductility as well as other physical properties that make for ease of fabrication by methods involving welding, bending and similar operations.

As pointed out in my co-pending application, Serial'No. 23,520, filed May 25, 1935, of which this is a division, it has long been common practice to cold roll iron and steel to obtain increased strength. However, cold rolling hasthe disadvantage that it lowers the corrosion resistance of the metal. Therefore, cold rolling is not applied where it is desired that the finished sheet or plate shall have a high resistance to corrosion, and, consequently, it has not been practical to produce cold rolled sheets and plates from special iron and steel alloys designed by reason of their composition to have high corrosion resistance. In other words, the sacrifice of corrosion resistance of these alloys has been such as to make it unattractive from the commercial standpoint to cold roll them to obtain high strength. Therefore, where it is desired to produce sheets andplates having both high corrosion resistance and high strength, resort has been had to special iron and steel alloys combining to a" greater or lesser extent the properties of high strength and corrosion resistance when the alloy is formed into sheets or plates by hot rolling.

Steel sheets of high strength have been produced by the alloying of iron with hardening elementscarbon, manganese, chromium, nickel, molybdenum, etc., but the fabrication by welding of such iron alloys has involved difllculties which have made them commercially undesirable for uses requiring their welding, and the maximum weldable limits of ferrous alloys hardened by additions of. one of the above elements, or combinations of these elements, established by the present welding technique is too low to permit more than ,moderate increases in strength.

Summarizing the above, sheets and light structural shapes formed from iron or steel alloys combining higher resistance to corrosion, high strength, and good welding properties; have not been available at a reasonable cost of production.

I have found that by appropriate selection of the iron or steel analysis with respect to workability and resistance to corrosion, and conducting the rolling operations in the manner hereinafter more particularly described, it is possible to produce sheets, platesand other relatively thin structural shapes having the high strength and other desirable physical properties that are ob-' tainable by cold rolling and at the same time either beneficially affect, or at least not materially decrease, the corrosion resistance properties of the, alloy ascompared with those that would be exhibited by a similar alloy worked by the hot rolling process.

By the term "cold rolling I mean a rolling operation carried on with the slab, plate or other body of metal in the cold state orat least at ,a temperature below the lower critical range at the beginning of the rolling operation, and in which the metal is brought at least to the state of hard-' ness known commercially as hard cold rolled. The comparison ofthe properties of such acold rolled sheet is made with those of a sheet of similar analysis that has been hot rolled and an;

healed or normalized. v The new product that I claim as my invention may be produced by selecting a copper-contain-i' ing iron or steel alloy, of the ferritic type'and bra suitable composition to exhibit resistance to corrosion and at the same time readily rollable when heated, and heating this alloy, in the form of a slab or billet of suitable thickness, to a temperature above or within the upper critical range and then rolling while accelerating the cooling of the metal by applying water or any other cooling medium, the combined rolling and cooling being continued until the metal has cooled or quenched to below the critical range. The rolling may be ical'range, in this way combining the effect. of cold rolling and quenching and imparting to the metal greater tensile and elastic strength with less loss of ductility to the piece than would result by either cold rolling or quenching applied individually. The rolling carried on after the metal is below the critical range does not appear to adversely afiect the corrosion resistance properties of the metal.

I have found that the rolling operation is advantageously carried out in a conventional threehigh rolling mill through which the pieces are passed to and fro. each side of the mill to catch the pieces as they are rolled and lift them into the return pass.

7 pieces being passed through the rolls. The proc- A tilting table is provided at continued after the temperature is below the critess can also be carried out on mills other than the conventional three-high rolling mill, for example, two-high or-four-high continuous mills,

providing the material is cooled and quenched during the rolling operation by the application of Water or other cooling medium.

The product may be produced from any one of a wide range of copper-containing iron and steel alloys of the non-austenitic or ferritic type. One of the advantages of the present invention resides in the fact that the product produced from relatively cheap iron and steel alloys will meet strength and corrosion resistance specifications that heretofore could only be met by resort to more expensive iron and steel alloys.

A group of relatively inexpensive corrosion resistant iron and steel alloys that are amenable to the process of my application Serial No. 23,520, and can be formed into sheets and plates having relatively high strength without detrimental effect on their corrosion resistance, are those copper-containing iron and steel alloys in which the carbon content is kept under 0.50%, the copper is under 0.80%, and phosphorus is less than 0.10%. I have found, for example, that improvement in strength values of the order noted below may be obtained by rolling a copper-bearing steel of the following analysis range under the conditions of accelerated quenching hereinbefore described:

Percent C 0.1 0.3 Mn 0.30 -0.70 S minus-0.04 P .06 -0.10 Cu 0.35 .50

Elastic Ultimate limit strength lbs/sq. in lbs/sq. in.

and, what is particularly important, these values are obtainable without adversely affecting the corrosion resistance of the alloy.

When the product is intended to be fabricated by welding, the proportion of carbon should be kept below about 0.30%, and should be proportionately lower if one or more other hardening elements are present in the analysis. By the term hardening element is meant any element which will cause the steel to become appreciably hardened by air quenching from around 2400 F., i. e., temperatures adjacent to the welding temperature zone.

Except to the extent that such alloys are excluded for uses requiring welding as above indicated, the product may be produced from commercially available copper-containing irons and steels of the ferritic type that contain, besides copper, greater or lesser amounts of one or more of the elements chromium, manganese, molybdenum, nickel, silicon, phosphorus and vanadium.

In carrying out the rolling operation the temperature at which the slab or other partially reduced shape is brought to the rolls will vary somewhat depending on the thickness of the slab and the thickness desired in the finished sheet or plate. The thickness of the slab brought to the rolling operation should also be considered in relation to the temperature, the extent of the reduction required and the time involved in effecting the reduction, so as to insure that a suitable relation is maintained between the rate of cooling of the material as it undergoes rolling and quenching and the rate of reduction to the desired thickness. In the case of heavier sheets, say, %"--1%" in thickness, the slab should be heated to about 2000 F., or well above the A03 critical range. Starting with a slab of say 1 -3" thick, reduction to about may be expected at the time the temperature of the slab or plate has fallen to the Ac: point, or around 1750 F. for a low carbon steel. The rolling and quenching should then be continued, the larger part of the further reduction occurring with the steel in the Aer-AC3 range. However, it is preferable to so conduct the operation as to insure that some further reduction must be effected after the temperature of the metal has fallen below the A01 range. In this way it is insured that there will not be any annealing effect which would tend to nullify the results of the accelerat ed cooling and rolling treatment. At, the same time, further improvement in the strength properties of the sheet is brought about in this final stage under conditions opproaching those of cold rolling but without the detrimental effects on the corrosion resistance of the product that is characteristic of cold rolling.

When starting with pieces that have already been brought down to a relatively thin cross-section by hot rolling, they may be brought to the combined quenching and rolling operation of the.

present invention at a temperature within the A03 critical range. For example, starting with steel sheets or break-downs that have been hot rolled to and which it is desired to reduce to sheets of 1%" thickness, the temperature at the beginning of the combined quenching and rolling operation may be about 1600 F.

While the invention has been described with particular reference to the production of sheets, it will be understood that beneficial results may be obtained in producing other products of thin cross-section such as light plates and strips. In fact, any structural shape that may be formed by rolling and having a cross-section of a similar thinness as sheets and light plates is to be considered as within the scope of the invention. Except where the context indicates a more restricted meaning, the term sheet as used in the specification and appended claims is to be understood as including plates and other structural shapes of thin cross-section.

The term slab as used in the specification is to be understood as including not only slabs as this term is applied in its more restricted sense in the rolling industry but also billets, plates and sheets which have been preliminarily worked by hot rolling from the original cast ingots, and which are intended to be further reduced to bring them to final dimension.

I claim:

1. As an improved article of manufacture, a rolled sheet of a corrosion resistant ferrous-base alloy of the ferritic type containing an effective amount but less than 0.8% copper, less than 0.5% carbon, and less than 0.1% phosphorus, said sheet having the corrosion resistance properties of a hot rolled sheet of like analysis, and said rolled sheet being further characterized by the strength properties and a physical structure such as is produced by heating said alloy to a temperature at least approximating the upper critical point, then simultaneously subjecting the alloy to rolling and quenching and continuing said combined rolling and quenching treatment until the temperature ,iiintu of the rolled product has been brought below the lower critical range.

2. As an improved article of manufacture particularly adapted to be fabricated by welding, a

rolled sheet composed of a copper-containing ferrous-base alloy of corrosion resistance analysis and of the ferritic type, containing hardening elements in an amount not exceedingsthe hardening equivalent of 0.3% carbon. said sheet having the corrosion resistance properties of a hot rolled sheet of like analysis, and said rolled sheet being further characterized by the strength properties and a physical structure such as is produced by heating said alloy to a temperature at least approximating the upper critical point, then simultaneously subjecting v the alloy to rolling and quenching and continuing said combined rolling and quenching treatment until the temperature of the rolled product has been brought below the lower critical range.

3. As an improved article of manufacture, a rolled sheet of a steel alloy of the ferritic type containing carbon (Ll-0.3%, sulphur less than 0.04%, phosphorus ODS-0.1%, and copper 0.35- 0.5%, said sheet having the corrosion resistance properties of a hot rolled sheet of like analysis, and said rolled sheet being further characterized by the strength properties and a physical 'structure such as is produced by heating said alloy to a temperature at least aproximating the upper critical point, then simultaneously subjecting the alloy to rolling and quenching and continuing said combined rolling and quenching treatment until the temperature of the rolled product has been brought below the lower critical range.

VICTOR H. LAWRENCE. 

